1 files changed, 30 insertions, 0 deletions
diff --git a/db/migrate/20211012015903_next_traversal_ids_sibling_function.rb b/db/migrate/20211012015903_next_traversal_ids_sibling_function.rb
new file mode 100644
index 00000000000..f32b8fc5a65
--- /dev/null
+++ b/db/migrate/20211012015903_next_traversal_ids_sibling_function.rb
@@ -0,0 +1,30 @@
+# frozen_string_literal: true
+
+class NextTraversalIdsSiblingFunction < Gitlab::Database::Migration[1.0]
+  include Gitlab::Database::SchemaHelpers
+
+  FUNCTION_NAME = 'next_traversal_ids_sibling'
+
+  def up
+    # Given array [1,2,3,4,5], concatenate the first part of the array [1,2,3,4]
+    # with the last element in the array (5) after being incremented ([6]).
+    #
+    # [1,2,3,4,5] => [1,2,3,4,6]
+    execute(<<~SQL)
+      CREATE OR REPLACE FUNCTION #{FUNCTION_NAME}(traversal_ids INT[]) RETURNS INT[]
+      AS $$
+      BEGIN
+        return traversal_ids[1:array_length(traversal_ids, 1)-1] ||
+        ARRAY[traversal_ids[array_length(traversal_ids, 1)]+1];
+      END;
+      $$
+      LANGUAGE plpgsql
+      IMMUTABLE
+      RETURNS NULL ON NULL INPUT;
+    SQL
+  end
+
+  def down
+    execute("DROP FUNCTION #{FUNCTION_NAME}(traversal_ids INT[])")
+  end
+end